pUA140 变形链球菌隐性质粒（Streptococcus mutans）BioVector NTCC典型培养物保藏中心

pUA140 质粒是一种小型隐性质粒，存在于变形链球菌（Streptococcus mutans）的一些菌株中，特别是 UA140 菌株。 “隐性”质粒指的是其功能并不立即显而易见，因为它不编码抗生素抗性等功能。

主要特征与功能

• 复制: pUA140 质粒通过一种称为**滚环复制（RCR）**的过程进行复制。它属于 pT181 质粒家族，其特点是在复制起始蛋白和复制起点方面存在相似性。

• 大小: 它是一种相对较小的质粒，大小约为 5.6 千碱基（kb）。

• 基因内容: 尽管最初被认为是隐性的，但研究已识别出几个开放阅读框（ORF）。一个特别重要的发现是，它编码一个毒素-抗毒素（TA）系统，这是一种确保其在细菌宿主内稳定存在的机制。

• 毒素-抗毒素系统: TA 系统是质粒的一种遗传“保险”。它由两个基因组成：一个稳定的毒素基因和一个不稳定的抗毒素基因。如果一个细菌在分裂后，子细胞没有继承 pUA140 质粒，不稳定的抗毒素就会降解，从而允许稳定的毒素杀死该细胞。这种“分离后杀伤”机制极大地促进了质粒在细菌群体中的持续存在。

研究与应用

pUA140 质粒的 TA 系统的发现对于理解质粒如何在细菌群体中持续存在具有重要意义。它被用作模型来研究：

• 质粒稳定性: TA 系统如何促进质粒的长期存活。

• 细菌遗传学: 像质粒这样的“自私”遗传元件如何演化并传播。

• 合成生物学: TA 系统可以被用于基因工程，作为一种负向选择工具，确保只有保留了所需质粒的细胞才能存活。

The BioVector™ pUA140 plasmid is a small, cryptic plasmid found in some strains of the bacterium Streptococcus mutans, specifically strain UA140. A "cryptic" plasmid means its function isn't immediately obvious, as it doesn't encode for things like antibiotic resistance.

Key Features and Function

• Replication: The pUA140 plasmid replicates via a process known as rolling circle replication (RCR). It belongs to the pT181 family of plasmids, characterized by similarities in their replication initiation protein and replication origins.

• Size: It's a relatively small plasmid, around 5.6 kilobases (kb).

• Gene Content: Although initially considered cryptic, research has identified several open reading frames (ORFs). A particularly important finding is that it encodes a toxin-antitoxin (TA) system, a mechanism that ensures its stability within the bacterial host.

• Toxin-Antitoxin System: The TA system is a genetic insurance policy for the plasmid. It consists of two genes: a stable toxin and a less stable antitoxin. If a bacterium divides and a daughter cell doesn't inherit a copy of the pUA140 plasmid, the unstable antitoxin will degrade, allowing the stable toxin to kill the cell. This "post-segregational killing" mechanism strongly favors the maintenance of the plasmid in the bacterial population.

Research and Applications

The discovery of the pUA140's TA system has been significant in understanding how plasmids persist in bacterial populations. It's used as a model to study:

• Plasmid stability: How TA systems contribute to the long-term survival of plasmids.

• Bacterial genetics: The evolutionary success and propagation of selfish genetic elements like plasmids.

• Synthetic biology: The TA system can be adapted for use in genetic engineering as a negative selection tool, ensuring that only cells retaining a desired plasmid will survive.

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